The present invention relates to an external operation handle device for circuit breakers, for example, molded case circuit breaker, earth leakage breaker, and the like.
An external operation handle device is used as an accessory device with a molded case circuit breaker, earth leakage breaker, etc. for conducting switching operation on a circuit breaker attached to a distribution board or a control board from outside the board.
An external operation handle device comprises a rotary handle grip and a slide base linked to the handle grip through a turn base, mounted on a mount base. In the state with the handle device mounted on a circuit breaker, the slide base is engaged with a locker handle of the circuit breaker and the handle grip is turned to drive the locker handle of the circuit breaker to ON and OFF positions through the turn base and the slide base.
Concerning an external operation handle device, Patent Document 1 discloses means, which enables to avoid a problem that a handle grip stops before reaching a TRIP indication position during movement from ON position towards the TRIP indication position in trip operation of the circuit breaker due to frictional drag against sliding of a movable mechanism of the handle device, and to assist correct indication of trip operation of the circuit breaker. Patent Document 1 discloses an assist mechanism comprising levers with rollers provided at both sides of a cam formed on the slide base, and a pressure is exerted by an urging spring through the rollers from a direction perpendicular to the moving direction of the slide base. The spring force acting on the tapered cam face forces the handle grip linked with the slide base to the TRIP indication position. The assisting mechanism is shown in FIGS. 5 through 8.
In those figures, reference numeral 1 designates a circuit breaker and numeral 2 designates an external operation handle device mounted on the circuit breaker 1. The circuit breaker 1 comprises a main casing 1a; a fixed contact 1b; a movable contact 1c; a switching mechanism 1d of a toggle linkage type; a locker handle 1e linking with the switching mechanism 1d and disposed at the top of the casing 1a; and an overcurrent tripping device 1f, all of which are installed in the main casing 1a. 
Switching operation of such a circuit breaker 1 is well known. When the locker handle 1e is turned from the ON position shown in FIG. 5 to the OFF position at the left side, the toggle link of the switching mechanism 1d is reversed and the movable contact 1c is opened receiving an urging force of the toggle spring. When an overcurrent is developed in the main circuit and then the overcurrent tripping device functions, the switching mechanism 1d trips and the movable contact 1c opens to automatically interrupt the current in association with the trip. In this trip operation, the locker handle 1e moves from the ON position to an intermediate position (trip indication position) between the ON position and the OFF position following the movement of the toggle linkage of the switching mechanism 1d and stops at this position.
The external operation handle device 2 comprises, as disclosed in detail in Patent Document 1, a mount base 3; a handle grip 4 of a rotary type; a turn base 5; a slide base 6; and a handle cover 7, that are mounted on the mount base 3. The locker handle 1e is engaged with the slide base 6 in conjunction with the handle device mounted on the circuit breaker 1 (FIG. 5).
The turn base 5 is connected to a shaft of the handle grip 4. The slide base 6 is located in the back surface side of the mount base 3. The slide base 6 is guided and supported so as to slide in the direction of opening and closing of the locker handle 1e. The slide base 6 is provided with an oblong hole opened in the central region of the slide base along the direction perpendicular to the sliding direction. A pin (crank pin) 5a provided on the turn base 5 is engaged with the oblong hole and links with the handle grip 4. At the back surface side of the slide base 6, handle arms 6a are projecting at either side of the locker handle 1e of the circuit breaker 1. A name plate 7a is affixed on the periphery of the top surface of the handle cover 7 and indicates positions of ON, TRIP, OFF and RESET of the handle grip 4.
When the handle grip 4 is manipulated to turn from the ON position to the OFF position, the slide base slides leftward from the position in FIG. 5 through the pin 5a of the turn base 5 shifting the locker handle 1e of the circuit breaker 1 to the OFF position through the handle arms 6a. 
The slide base 6 is provided with an assisting mechanism, as disclosed in Patent Document 1, comprising a cam and a pressing lever that makes the rollers contact with tapered cam faces at left and right sides of the cam and exerts a spring force pushing against the tapered cam faces. As shown in detail in FIG. 8, a cam 6b is formed on the back surface of the slide base 6, and a pair of levers 8b pivotally supported with a screw 8a at one end thereof is provided at both sides of the cam 6b in left and right side region of the mount base 3. The rollers (bearings) 8c provided on the levers 8b push the cam face 6b-1 by the spring force of urging springs 8d. 
When the circuit breaker 1 trips, the slide base 6 pushed by the locker handle 1e starts to move leftward from the position (ON position) in FIG. 8. In a middle of the movement, the rollers 8c in contact with the cam 6b comes to the tapered portion of the cam face, where the slide base 6 receives a leftward driving force by the spring force of the urging spring 8d. Thus, the handle grip 4 of the external operation handle device 2 moves from the ON position to the TRIP position shown in FIG. 7 indicating trip operation of the circuit breaker.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2005-149918
The conventional assisting mechanism provided in an external operation handle device, however, involves problems of high production costs due to a large number of parts including pairs of levers 8, rollers 8c, and urging springs 8d, and large number of steps for their assembly. Furthermore, the size of the external operation handle device has to be large enough to ensure a space occupied by these parts in the mount base 3.
The invention provides an external operation handle device for a circuit breaker having an assist mechanism with improved structure to reduce the number of parts and steps for assembling, and down-sized and compact structure of the device.
Further objects and advantages of the invention will be apparent from the following description of the invention.